[−][src]Trait ndless::error::Error
Error
is a trait representing the basic expectations for error values,
i.e., values of type E
in Result<T, E>
. Errors must describe
themselves through the Display
and Debug
traits, and may provide
cause chain information:
The source
method is generally used when errors cross "abstraction
boundaries". If one module must report an error that is caused by an error
from a lower-level module, it can allow access to that error via the
source
method. This makes it possible for the high-level module to
provide its own errors while also revealing some of the implementation for
debugging via source
chains.
Provided methods
fn description(&self) -> &str
This method is soft-deprecated.
Although using it won’t cause compilation warning,
new code should use Display
instead
and new impl
s can omit it.
To obtain error description as a string, use to_string()
.
Examples
match "xc".parse::<u32>() { Err(e) => { // Print `e` itself, not `e.description()`. println!("Error: {}", e); } _ => println!("No error"), }
fn cause(&self) -> Option<&dyn Error>
replaced by Error::source, which can support downcasting
The lower-level cause of this error, if any.
Examples
use std::error::Error; use std::fmt; #[derive(Debug)] struct SuperError { side: SuperErrorSideKick, } impl fmt::Display for SuperError { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { write!(f, "SuperError is here!") } } impl Error for SuperError { fn description(&self) -> &str { "I'm the superhero of errors" } fn cause(&self) -> Option<&Error> { Some(&self.side) } } #[derive(Debug)] struct SuperErrorSideKick; impl fmt::Display for SuperErrorSideKick { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { write!(f, "SuperErrorSideKick is here!") } } impl Error for SuperErrorSideKick { fn description(&self) -> &str { "I'm SuperError side kick" } } fn get_super_error() -> Result<(), SuperError> { Err(SuperError { side: SuperErrorSideKick }) } fn main() { match get_super_error() { Err(e) => { println!("Error: {}", e.description()); println!("Caused by: {}", e.cause().unwrap()); } _ => println!("No error"), } }
fn source(&self) -> Option<&(dyn Error + 'static)>
The lower-level source of this error, if any.
Examples
use std::error::Error; use std::fmt; #[derive(Debug)] struct SuperError { side: SuperErrorSideKick, } impl fmt::Display for SuperError { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { write!(f, "SuperError is here!") } } impl Error for SuperError { fn description(&self) -> &str { "I'm the superhero of errors" } fn source(&self) -> Option<&(dyn Error + 'static)> { Some(&self.side) } } #[derive(Debug)] struct SuperErrorSideKick; impl fmt::Display for SuperErrorSideKick { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { write!(f, "SuperErrorSideKick is here!") } } impl Error for SuperErrorSideKick { fn description(&self) -> &str { "I'm SuperError side kick" } } fn get_super_error() -> Result<(), SuperError> { Err(SuperError { side: SuperErrorSideKick }) } fn main() { match get_super_error() { Err(e) => { println!("Error: {}", e.description()); println!("Caused by: {}", e.source().unwrap()); } _ => println!("No error"), } }
Methods
impl dyn Error + 'static
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pub fn is<T: Error + 'static>(&self) -> bool
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Returns true
if the boxed type is the same as T
pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T>
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Returns some reference to the boxed value if it is of type T
, or
None
if it isn't.
pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T>
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Returns some mutable reference to the boxed value if it is of type T
, or
None
if it isn't.
impl dyn Error + Send + 'static
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pub fn is<T: Error + 'static>(&self) -> bool
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Forwards to the method defined on the type Any
.
pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T>
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Forwards to the method defined on the type Any
.
pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T>
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Forwards to the method defined on the type Any
.
impl dyn Error + Send + Sync + 'static
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pub fn is<T: Error + 'static>(&self) -> bool
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Forwards to the method defined on the type Any
.
pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T>
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Forwards to the method defined on the type Any
.
pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T>
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Forwards to the method defined on the type Any
.
impl dyn Error
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pub fn downcast<T: Error + 'static>(
self: Box<Self>
) -> Result<Box<T>, Box<dyn Error>>
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self: Box<Self>
) -> Result<Box<T>, Box<dyn Error>>
Attempt to downcast the box to a concrete type.
impl dyn Error + Send
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pub fn downcast<T: Error + 'static>(
self: Box<Self>
) -> Result<Box<T>, Box<dyn Error + Send>>
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self: Box<Self>
) -> Result<Box<T>, Box<dyn Error + Send>>
Attempt to downcast the box to a concrete type.
impl dyn Error + Send + Sync
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pub fn downcast<T: Error + 'static>(
self: Box<Self>
) -> Result<Box<T>, Box<Self>>
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self: Box<Self>
) -> Result<Box<T>, Box<Self>>
Attempt to downcast the box to a concrete type.
Implementations on Foreign Types
impl Error for ParseBoolError
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fn description(&self) -> &str
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fn cause(&self) -> Option<&dyn Error>
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replaced by Error::source, which can support downcasting
fn source(&self) -> Option<&(dyn Error + 'static)>
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impl Error for Utf8Error
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fn description(&self) -> &str
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fn cause(&self) -> Option<&dyn Error>
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replaced by Error::source, which can support downcasting
fn source(&self) -> Option<&(dyn Error + 'static)>
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impl Error for ParseIntError
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fn description(&self) -> &str
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fn cause(&self) -> Option<&dyn Error>
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replaced by Error::source, which can support downcasting
fn source(&self) -> Option<&(dyn Error + 'static)>
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impl Error for TryFromIntError
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fn description(&self) -> &str
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fn cause(&self) -> Option<&dyn Error>
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replaced by Error::source, which can support downcasting
fn source(&self) -> Option<&(dyn Error + 'static)>
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impl Error for TryFromSliceError
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fn description(&self) -> &str
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fn cause(&self) -> Option<&dyn Error>
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replaced by Error::source, which can support downcasting
fn source(&self) -> Option<&(dyn Error + 'static)>
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impl Error for ParseFloatError
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fn description(&self) -> &str
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fn cause(&self) -> Option<&dyn Error>
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replaced by Error::source, which can support downcasting
fn source(&self) -> Option<&(dyn Error + 'static)>
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impl Error for FromUtf8Error
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fn description(&self) -> &str
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fn cause(&self) -> Option<&dyn Error>
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replaced by Error::source, which can support downcasting
fn source(&self) -> Option<&(dyn Error + 'static)>
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impl Error for FromUtf16Error
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fn description(&self) -> &str
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fn cause(&self) -> Option<&dyn Error>
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replaced by Error::source, which can support downcasting
fn source(&self) -> Option<&(dyn Error + 'static)>
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impl Error for ParseError
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fn description(&self) -> &str
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fn cause(&self) -> Option<&dyn Error>
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replaced by Error::source, which can support downcasting
fn source(&self) -> Option<&(dyn Error + 'static)>
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impl Error for DecodeUtf16Error
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fn description(&self) -> &str
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fn cause(&self) -> Option<&dyn Error>
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replaced by Error::source, which can support downcasting
fn source(&self) -> Option<&(dyn Error + 'static)>
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impl Error for Error
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fn description(&self) -> &str
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fn cause(&self) -> Option<&dyn Error>
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replaced by Error::source, which can support downcasting
fn source(&self) -> Option<&(dyn Error + 'static)>
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impl Error for BorrowError
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fn description(&self) -> &str
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fn cause(&self) -> Option<&dyn Error>
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replaced by Error::source, which can support downcasting
fn source(&self) -> Option<&(dyn Error + 'static)>
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impl Error for BorrowMutError
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fn description(&self) -> &str
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fn cause(&self) -> Option<&dyn Error>
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replaced by Error::source, which can support downcasting
fn source(&self) -> Option<&(dyn Error + 'static)>
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impl Error for CharTryFromError
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fn description(&self) -> &str
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fn cause(&self) -> Option<&dyn Error>
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replaced by Error::source, which can support downcasting
fn source(&self) -> Option<&(dyn Error + 'static)>
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impl Error for ParseCharError
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fn description(&self) -> &str
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fn cause(&self) -> Option<&dyn Error>
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replaced by Error::source, which can support downcasting
fn source(&self) -> Option<&(dyn Error + 'static)>
[src]
Implementors
impl Error for ndless::io::Error
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fn description(&self) -> &str
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fn cause(&self) -> Option<&dyn Error>
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fn source(&self) -> Option<&(dyn Error + 'static)>
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impl Error for StripPrefixError
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fn description(&self) -> &str
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fn cause(&self) -> Option<&dyn Error>
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replaced by Error::source, which can support downcasting
fn source(&self) -> Option<&(dyn Error + 'static)>
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impl Error for SystemTimeError
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fn description(&self) -> &str
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fn cause(&self) -> Option<&dyn Error>
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replaced by Error::source, which can support downcasting